Sudden cardiac death is the leading cause of death in the United States. Most sudden cardiac death is caused by ventricular fibrillation (“VF”), in which the muscle fibers of the heart contract without coordination, thereby interrupting normal blood flow to the body. The only known treatment for VF is electrical defibrillation, in which an electrical pulse is applied to a patient's heart. The electrical shock clears the heart of the abnormal electrical activity (in a process called “defibrillation”) by depolarizing a critical mass of myocardial cells to allow spontaneous organized myocardial depolarization to resume.
One way of providing electrical defibrillation is by automatic or semi-automatic external defibrillators, collectively referred to as “AEDs,” which send electrical pulses to a patient's heart through electrodes applied to the torso to defibrillate the patient or to provide for external pacing of the patient's heart. The use of AEDs by untrained or minimally trained operators for a patient in sudden cardiac arrest is a time critical operation. The electrical pulse must be delivered within a short time after onset of VF in order for the patient to have any reasonable chance of survival.
Thus, simplifying and minimizing the number of steps required by the operator to defibrillate and improving the reliability of defibrillation increases key aspects of an AED design. The AED is typically stored with electrodes that are sealed in an enclosure that protects the electrodes from contamination and retards desiccation. Before defibrillation can commence the operator must open the enclosure, remove the electrodes, and apply them to the patient. Electrodes that are sealed with a connector inside an enclosure, such as a bag, can require multiple steps by the operator. First, the operator must open the sealed bag. Second, the operator must plug the electrodes into the AED. Third, the operator must remove a release liner, which typically covers a gel on the electrode pads from the first electrode and fourth, the operator must place the electrode on the patient. The operator must then repeat the fourth step with the second electrode and place the second electrode on the patient.
The electrodes typically comprise a non-conductive base layer such as a plastic disc and a conductive layer that distributes the current transmitted to the electrode by the defibrillator. The base layer is typically constructed of a thin, flexible polymeric material such as urethane foam, or a polyester or polyolefin laminate which is electrically insulating and provides structural integrity to the electrode. Conventionally, such electrodes further include a layer of adhesive material that is used to adhere the electrode to the patient's chest prior to and during delivery of the shocks. The adhesive material is typically a viscous water-based gel material that contains ionic compounds which increase the material's electrical conductivity to provide a low resistance path for current to flow from the electrode to the patient's chest.
As is known in the art, electrodes used with automatic external defibrillators often are stored for relatively long periods of time until needed. During this time, the adhesive material can become desiccated. This desiccation decreases the effectiveness of the material in that it lowers the material's conductivity, which in turn raises the impedance at the contact area between the electrode and the skin. This increased impedance results in less current reaching the heart. Due to the problem of desiccation, the adhesive material normally is covered with a removable backing that reduces the material's exposure to air. Despite the provision of such backings, however, conventional adhesive materials still tend to dry out. For the purpose of preventing such desiccation, modern medical electrode packaging typically provides a sealed electrode storage environment and through-wall electrical connectivity to electrotherapy devices such as external defibrillators. The electrode packaging is typically either a flexible, heat-sealable laminate material, or a rigid, molded plastic material, both of which serve as a moisture barrier.
Flexible electrode housings such as foil-lined plastic bags provide economical and simple packaging for electrodes in many instances. Electrode wires may extend through the exteriors of known flexible housings, and connect directly to electrotherapy devices. A seal around the wires is typically achieved by heat-sealing the packaging material to the wires or by molding a plastic piece around the wires and sealing the packaging material to the piece. The electrodes themselves are typically arranged in the package so that they form an electrical circuit between themselves and the associated medical device. Prior art flexible housings, however, suffer from several drawbacks. Electrode function or sterility, for instance, may be compromised when electrode wiresets protrude through the flexible housing. For example, flexing may weaken the bond between the electrode wireset and the flexible material. In addition, the flexible material of the packaging may remain adhered to the electrode wires after placement of the electrodes on a patient, causing user confusion or delay. Further, adequately sealing areas where the electrode wires extend through flexible housings continues to present challenges and may increase manufacturing costs or complexity.
Rigid structures offer an alternative to flexible housings. Walls of rigid structures may include insert-molded electrical contacts, such as pins, which provide through-wall electrical connectivity between enclosed electrode wires and external electrotherapy devices. Thus, the electrode wires do not exit the cartridge, but rather, are permanently attached to electrical contacts that pass through the wall of the rigid structure. These electrical contacts complete the electrical connection to the intended device. Although rigid housing structures may sometimes be more expensive and have higher manufacturing costs than flexible housings, rigid structures are often selected because they have been designed to enclose electrode wiresets without compromising the seals of the structure, and they offer relatively simple user interfaces. Rigid structures, however, may be less desirable in some applications, such as at high altitudes, when pressures inside the structures greatly exceed ambient pressures. Also, heat-seal film, which is often stretched over rigid structure openings, may be vulnerable to puncture.
In addition to these disadvantages, these prior art electrode packaging materials, whether rigid or flexible, are external to the electrode and must be disengaged from the electrodes prior to deployment of the electrodes. For instance, prior art packaging comprising a flexible, heat-sealable pouch or envelope-style structure must be torn and removed and any sort of release liner or backing material adhered to the conductive gel must be stripped away in two separate steps. These are steps which reduce the efficiency of the device operator during a life-saving process such as cardiac defibrillation. There is a long-standing need for an electrode storage system that is integrated within and is part of the electrode itself and that prevents desiccation of the electrically conductive gel materials contained therein. Such a self-storing electrode would allow for long-term sealed storage of the electrodes and ease of operation of the electrodes without the limitations of prior art flexible and rigid housings, particularly flexible housings that must be torn off prior to use. In addition, such self-storing electrode would be useful in a wide array of applications for both receiving and transmitting current such as, for example, in cardiac defibrillation.